Miniaturization really starts to stress fine motor control. When you have people putting together your boards/etc, people can do board repairs. When you have people assembling the final product, people can replace components. When you have machines doing everything from surface mount part placement, to being part of the assembly process itself, it becomes a lot harder.
I'll happily do work on stuff from the 80s, soldering included. 90s starts to get sketchy for me because my surface mount work is sloppy. Once you get into the 00s, things start getting packed to the point that fewer and fewer people have the practice and fine motor control to do board work. The GameCube is pretty packed on the boards for example, I had "fun" doing a region mod on mine. Fast forward to today, and assemblies are packed to the point where the same is now true for component replacements, where fine motor control is needed to disassemble things properly. While there's still stuff you can do to customize some stuff, making a custom case for a PS4 is a lot different than repairing a PS4.